We can call it a jungle or wild wild west, every social media now has some form of crypto scams. However, Facebook is such well known that scammers are using it to scams and it's hard to stop it even if they say that they have either bot or manual to review every ad. And there are a lot of forms of scams, even a hack Facebook account can turn into scams without them knowing it.
And remember this, it's because Facebook are business entity, and so scammers are just going to pay them and we can all say that even if they deny it, they doesn't care as long as they are making money.
How can they police their marketplace for example?